Classification of granular materials



Dec. 9, 1969 A. T. LOVEGREEN 3,

CLASSIFICATION OF GRANULAR MATERIALS Filed May 10. 1967 5 Sheets-Sheet 1 ANGULARLY ADJUSTABLE IN VENT O R HM/V TREVOR LOVEGREE/V ATTORNEYS Dec. 9, 1969 A. T. LOVEGREEN 3,432,691

CLASSIFICATION OF GRANULAR MATERIALS Filed May 10. 1967 5 Sheets-Sheet 3 6104/ max/01a iol/E GRE EN ATToRA Ey s mam/ 1969 A. T. LOYEGREEN 3,

CLASSIFICATION OF GRANULAR MATERIALS Filed May 10. 19s? 5 Sheets-Sheet 4 IIVVEIVTOR2 ALM/ TREV R LOVE GREEN By: Mr, aw Mk MUM/E75 Dec. 9, 1969 A. T. LOVEGREEN CLASSIFICATION OF GRANULAR MATERIALS I 5 Sheets-Sheet 5 Filed May 10. 1967 a QxQfi QmQ Q N fiA/T 012- HUW RE V K Love Galas/v Wf Mi W United States Patent 3,482,691 CLASSIFICATION OF GRANULAR MATERIALS Alan Trevor Lovegreen, 16 Church Lane, Wallingford, England Filed May 10, 1967, Ser. No. 637,555 Claims priority, application Great Britain, May 11, 1966, 20,767/66; June 3, 1966, 24,740/66 Int. Cl. B03d l/14, 1/00 US. Cl. 209-156 14 Claims ABSTRACT OF THE DISCLOSURE Crushed mineral ores or like granular material of mixed particle densities are separated on a horizontal plane separating surface by establishing a laminar flow of processing liquid from a liquid discharge orifice located above the separating surface, and feeding the starting material mixture into the flow. The head of processing liquid is held constant at a value such that a standing wave pattern is established on the separating surface at a finite distance from the axis of the orifice and from which the denser particles are deposited while the less dense particles are deposited beyond the standing wave. The surface may be static or continuously moving at constant speed, and more than one liquid discharge orifice may be located at intervals over the surface for successive action on the deposited particles to increase the concentration of the dense and less dense particles, or their spatial separation, or both.

This invention relates to the classification or beneficiation of granular materials, and particularly to the separation of mixtures of heavy and light minerals fractions. The problem of such separations frequently arises when mixtures of granular materials contain particles of different densities but approximately the same size, so that efiicient separation by sieving is impracticable. A typical example of the difficulty of such separations occurs in mixtures of fine rock grains such as sand and coal, or wolframite and cassiterite.

The present invention is based on the observation that grains of rock carried along in a stream of liquid will travel at velocities proportional to their weights, and will gravitate to the bottom of the stream where they will settle on the surface of the form containing the stream, whether this be a natural river or artificial channel, fiume or duct. Having settled, the particles or grains move in the form of transverse ripples, each of which is a small mound of grains which continually climb over each other. Sometimes the grains move by a saltatory motion in which a grain jumps for a short distance, settles temporarily, and then jumps again.

Observation of this phenomenon reveals that particles of equal size but different weights move at different rates, the lighter particles moving faster than the heavier ones and that variations in flow give rise to different ripple shapes.

It can further be demonstrated that a high velocity stream of water impinging vertically on a fiat horizontal free surface establishes, adjacent the point of impingement, a fast-moving film or lamina of water which spreads free of constraint radially over the surface and then breaks down in a circular zone of turbulence known as a standing wave or hydraulic jump. Beyond this zone the water spreads further more quietly. If granular material is entrained in the stream, an annular ripple of solids forms at the standing wave. If this material is a mixture of particles having different densities, those of greater density will remain while those of less density will rise over them to form a second annular ripple downstream 3,482,691 Patented Dec. 9, 1969 ice of the first ripple. Depending on the nature of the materials in the mixture separation may be complete, or the degree of separation may vary. Normally, the heavy fraction tends to concentration whereas the less dense fraction may be contaminated by a proportion of dust and small particles of the heavy fraction.

The present invention makes use of the observed phenomena to separate light from heavy particles of approximately the same size by setting up a ripple of each under controlled conditions. The first or upstream ripple will then consist predominantly of the heavy fraction and the second or downstream ripple will consist predominantly of light particles.

According to the present invention, therefore, a mixture of granular materials containing a light and a heavy fraction is separated into its constituent fractions by placing it on a flat and generally horizontal separating surface and exposing it to a lateral and initially laminar stream of liquid which flows over the surface at a velocity sufficient to cause migration of the particles to a zone of turbulent breakdown of the laminar flow, or standing wave, so as to set up a ripple of heavy particles at this zone followed by a ripple of light particles and, once these two ripples have been formed, preventing the ripples from multiplymg.

Prevention of the multiplication of ripples can be achieved in either of two ways:

(1) By slowing or stopping the flow of liquid, or

(2) By continuous displacement of the separating surface in its own plane. A batch process for treating successive batches of a mixture of heavy and light granular materials may control ripple multiplication by employing alternative (1) above, whereas a continuous process may employ alternative (2) above, as will be described below.

During exposure of the particles to the lateral stream, the upstream ripple may be disturbed, as by continuous or intermittent raking, to uncover any particles of light material which have become embedded in the mass of heavy particles. Alternatively, the separating surface may be traversed in its own plane past one or more clean liquid discharge nozzles.

Preferably, the mixture to be classified or beneficiated is introduced onto the separating surface as a slurry, the liquid phase of which constitutes the liquid which sets up the standing wave pattern.

In one form of the invention, the mixture is placed at the centre of the separating surface as part of a vertically downward jet of water or other suitable liquid which spreads out radially, and initially as laminar flow, over the surface. This radial laminar flow then breaks down in a concentric circular standing wave and establishes an inner or upstream annular ripple of heavy particles and an outer or downstream annular ripple of light particles. The flow may be continued without solids until the inner ring has been cleaned of light fractions, then the two ripples can be separated into respective receptacles by cutting off the vertical jet and washing the ripples in opposite directions by means of a vertical annular curtain of clean liquid caused to impinge on the separating surface between them.

For a given rate of water flow the diameters of the annuli are constant but depend to some extent on the nature of the separating surface. The rate of flow depends on the diameter of the jet pipe, the head of water, and the gap between the mouth of the jet pipe and the separating surface. Too small a gap causes a valve effect which reduces the flow. So long as the gap is greater than a certain minimum value, the diameters of the annular ripples are substantially independent of gap size, but the flow is smoother at smaller sizes. If the supply of solids is cut off, but the water jet allowed to continue at the same rate of flow, the annular ripples of solids reach a maximum diameter, the separation between the annuli being variable in dependence on the nature of the solids.

By selectively reducing or blanking off parts of the annular gap between the mouth of the jet pipe and the separating surface, the geometrical pattern of the ripples can be changed. Similarly, a change in the angle between the axis of the jet pipe and the separating surface produces a corresponding change in the geometrical pattern. A jet pipe whose axis is at an angle other than 90 to the surface, but the plane of whose mouth is parallel to the plane of the surface produces an egg-shaped ripple pattern, whilst a pipe of cross-section other than circular gives a standing wave form related to the shape of the orifice. These conditions afford additional facilities for the control of the separation process.

In another form of the invention the mixture to be classified is fed onto a continuously moving belt which provides the separating surface across which is established at least one transverse jet of liquid which, on impinging on the belt surface, establishes initial laminar flow. This jet will set up two generally parallel ripples which can be separated in any convenient manner.

In yet another form of the invention the mixture to be classified is continuously fed as a slurry through a vertical or inclined nozzle which discharges a jet of slurry close to the belt. The mixture is thus entrained in the resultant initial radial laminar flow over the surface of the moving belt.

Advantageously, two or more successive jets are established in close juxtaposition above the belt surface to increase both the spatial and the grading separation of the particles. If desired, each ripple may then be further exposed to a respective transverse jet caused to impinge on the belt surface between the ripples, the jets being oppositely directed so as both to increase further the spatial separation of the main ripples and to further grade each ripple, which thus becomes divided into two. The two outer ripples then consist of light fraction particles and the two inner ripples of heavy fraction particles. The respective pairs of ripples can be recombined to give two separate fractions.

The texture of the surface which supports the particles during the separation process is not critical, but variation of the coefficient of friction of the separating surface results in changes in the spatial separation of the ripples.

The invention also includes apparatus for carrying out the process of separation.

A practical embodiment of each of the above-mentioned forms of the invention will now be described, by way of illustration only thereof, with reference to the accompanying generally schematic drawings in which:

FIGURE 1 is a perspective view of a first embodiment;

FIGURE 1A is a plan view of part of the machine of FIGURE 1;

FIGURE 1B is a sectional view of a funnel; 7

FIGURE 2 is a diagram showing the operation of the machine of FIGURE 1;

FIGURE 3 is a diametral sectional elevation of a sec ond form of machine;

FIGURE 4 is a perspective view, partly broken away, of the machine of FIGURE 3 showing the parts in a different position, and

FIGURE 5 is a schematic perspective view of a third form of machine.

Referring first to FIGURES 1 and 1A of the drawings, the separating surface is constituted by the horizontal top flight of a continuous conveyor belt which is driven at constant speed, and moves in the direction of the arrow 11. The top flight 10 is supported on a flat bed plate 12 which underlies almost the whole of the flight and is carried on a frame structure 13 built up from longitudinal and transverse rectangular section tubes the interiors of which intercomrnunicate to form a continuous plenum chamber. At each junction of a pair of tubes a bearing p ate 14 is welded, partly to reinforce the junction but mainly to act as pads and anchorage points for the plate 12. Each bearing plate 14 is drilled through to form a port 15 which registers with a port 16 in the bed plate 12. An external header 17 opens into the hollow frame 13 and is connected by a flexible pipe 18 to a source (not shown) of air at relatively low pressure.

The operation of the construction described so far is as follows:

The belt is driven at the desired speed so that its top flight 10 runs over the surface 'of the bed plate 12. Air supplied through the header 17 fills the hollow frame 13 at low pressure and escapes through the ports 15 in the bearing plates 14 and the registering ports 16 in the bed plate 12 and escapes between the plate and the underside of the top flight 10 so as to form an air bearing over at least the greater part of the area of the bed plate 12. Thus the frictional drag of the belt on the bed plate is minimised.

The belt runs over a drive roller 20, a head drum 21 and an idle roller 22 below the drive roller 20. Pulleys and belts 23 provide the drive to the shaft of the drive roller 20. A tray 24 underlies the return flight 25 of the belt to collect liquid and any other matter dripping therefrom and channel it to a drain 26. The entire frame structure 12, 13,

14, and belt assembly 10, 20 26, and superstructure (to be described) is supported in cantilever fashion on a pedestal 27.

The superstructure referred to above consists of a main feed unit for the mixture to be separated and water or other processing liquid (assumed for convenience hereinafter to be water), and a subsidiary array 31 of processing jets or nozzles. The main feed unit comprises an initial constant head water tank 32 having main supply inlets 33 and containing funnels 34 having adjustable weirs 35 around the rims of their conical bowls. Outlets 36 from the base of the constant head tank 32 supply separate flow stabilising tanks 37, 38. Each funnel 34 discharges into a common overflow pipe 39. The tanks 32, 37 and 38 are carried on a common subframe 40 secured to the pedestal 27.

The tank 37 contains a feed funnel 41 into which the .mixture to be separated can be fed simultaneously with the flow of water from the tank 37 over an adjustable weir 42 similar to the weirs 35. The orifice of the discharge pipe 43 from the feed funnel 41 lies just above the surface of the top flight 10 of the belt.

The tank 38 contains a. similar funnel 44 to that shown at 41, having an adjustable weir 45 and a discharge pipe 46 whose orifice is spaced by a short gap above the surface of the top flight 10 of the belt. This funnel 44 supplies processing water as will be described below.

The positions of the two discharge pipes 43, 46 are nominally fixed in relation to the centre-line of the top flight 10 and to each other, but fine adjustment is provided by means of adjusting screws 47, 48, respectively mounted in end flanges 49, 50 on the subframe 40. These adjusting screws bear on the respective tanks 37, 38, and in order to accommodate the necessary fine adjustments, each supply pipe 36 has a flexible section indicated at 51.

The array 31 of nozzles consists of two pairs of nozzles 52, 53 carried on respective crossbars 54, 55 which in turn are supported on a longitudinal boom 56 anchored at one end to the subframe 40 and at the other end to an end frame 57. The nozzles are fed with processing water through hoses 58 and are adjustable for position and angle on their respective crossbars.

Along each side of the frame .13 are mounted collecting troughs 60, 61 (only one of each is visible in FIG- URE 1) whose open mouths register with sections of the belt flight 10 to zeceive material washed oh the belt by the processing water from the pipe 46 or the nozzles 52, 53. Fine light particles, commonly known as tailings, are collected in the trough 60 and coarser and heavier particles, usually termed middlings, are cola lected in the trough 61 for subsequent disposal according to requirements.

Referring now to FIGURE 2 of the drawings, which is a diagram of the essential part only of the machine of FIGURE 1, the mixture M of solids to be separated is fed into the feed funnel 41 at the same time as water from the tank 37 (here represented for convenience as a pipe 37a) to form a slurry. The rates of feed of solids and water are preferably adjusted to give a slurry at the discharge orifice 43 containing about l7%20% solids, but other proportions can be adopted at will.

As the slurry strikes the surface of the top flight 10 of the belt it spreads radially in all directions as indicated by the arrows L and travels initially outwards in a laminar flow of water. At the zone R this laminar flow breaks down and a turbulent standing wave pattern is formed. The radial velocity of the water decreases suddenly and the Water piles up in a wave profile, continuing to spread beyond the turbulent zone R at a slower and diminishing speed. If the separating surface 10 were stationary, the turbulent zone R would be circular and of constant radius so long as the input conditions remained constant. Since, however, the belt is moving in the direction of the arrow 11, the circular pattern is distorted and only short arcs on the ends of the transverse diameter D, remain substantially circular. Ahead (relative to the travel of the flight 10) of the feed orifice 43, over a large arc centred about the centre-line C of the moving separating surface 10, the shape of the standing wave R in plan is flattened, whilst downstream thereof the shape is elongated, these distortions being substantially trigonometrical functions of the belt speed.

In the turbulent zone R, heavy particles are deposited in a ripple while less dense particles jump over this ripple and are deposited in a similarly contoured ripple beyond. Since the separating surface 10 is moving, these ripples tend to form ribbons stretching parallel to the axis C of the flight 10 from the ends of the transverse diameter D However, over a large arc ahead of the feed orifice 43, the ripples become compressed and the turbulence is increased, resulting in a lateral dissipation of the solids towards the ends of the diameter D the system settling down to equilibrium conditions governed by the velocity of the laminar radial flow, the composition of the mixture, and the speed of travel of the separating surface 10.

Beyond the feed orifice 43, the ripples remain largely unseparated, due to the removal of the deposited particles from the influence of the laminar flow before steady deposition conditions can be established. This unseparated material is represented on FIGURE 2 at S.

The processing funnel 44 is supplied with water from the tank 38 (represented in FIGURE 2 by a pipe 38a) and is meanwhile discharging water onto the moving separating surface through its orifice 46 and establishes a distorted turbulent zone T of similar pattern in plan to that of the feed orifice 43. When the first deposited particles in the zone S reach this turbulent zone T, they begin to pile up, and a similar lateral dissipation occurs as takes place ahead of the feed orifice 43. The denser particles are moved less than the less dense particles, so that they reinforce the dense ribbon which started at the ends of the transverse diameter D The less dense particles also begin to accumulate in this ribbon, but as they come progressively under the influence of the flow from the orifice 46 they are carried to the outer boundary of the ribbon.

By the time the first deposits of particles in the unseparated zone S have been carried by the joint action of the flow from the orifice 46 and the motion of the separating surface 10 to the vicinity of the ends of the transverse diameter D of the laminar flow pattern of the orifice 46, the partly formed ribbon comes under the full influence of the standing wave action and separation of the particles proceeds. As a result, two distinct and concentrated ribbons of dense particles A and less dense particles B emerge, the degree of physical separation between them varying from zero to a finite distance depending on various factors including the surface texture of the flight 10 and the characteristics of the constituents of the mixture, including density and crystal shape.

As the concentrated ribbons of particles A and B move with the belt away from the influence of the concentrating flow from the orifice 46, they come under the influence of the flow pattern from the nozzles 52. These are set to impinge on the belt at or near the line of demarcation between the ribbons A and B and create similar flow patterns to those set up by the feed orifice 43 and the concentrating flow orifice 46. When the ribbons encounter the standing wave formation from the respective nozzle, they are parted, the dense particle ribbons A moving towards the centre of the belt and the less dense particle ribbons B moving away from the centre. By suitably inclining the nozzles 52 in the transverse plane, the dense particle ribbons A can be brought together in a single central ribbon A while the ribbons B can be moved outwards towards the edges of the belt to form widely spaced less dense particle ribbons B At this stage also some further separation of particles from each ribbon may occur. If this happens, the less dense ribbons B will be more concentrated due to loss of any residual least dense particles, but the concentration of the final dense ribbon A is unaffected because the less dense constituents in the ribbon A are pushed towards the centre and so recombine with the single cen tral dense ribbon A As shown in FIGURE 1, more than one pair of opposed segregating jets can be used. Alternatively, or in addition, a second concentrating funnel can be mounted beyond the funnel 44 to subject the ribbons A B to a further separating action. The least dense particles are carried over the edge of the belt, as indicated by the arrows 60a, 61a in FIGURE 2, into the tailings and middlings troughs 60, 61 (see FIGURE 1).

If the recovered dense particle material is still too rich in less dense particles, the ribbon A may be recycled or passed through another similar machine.

From the foregoing description, it will be seen that it is possible for a single machine constructed in accordance with FIGURE 1 of the drawings to produce three fractions from a starting mixture, any one or more of which may be wanted. Concentration of each can be further increased by recycling that fraction alone, if necessary, changing the belt speed, the hydraulic head at the funnels 41, 44, or the gap between the feed orifice 43 or the concentration orifice 46 and the separating surface 10, or any combination of these parameters.

The angle between the axis of the feed orifice 43 or the concentration orifice 46, or both, and the separating surface 10 can be made variable, and results in changes of the pattern of ripple formation. It has already also been indicated that the nature of the flow from each orifice is controllable by adjustment of the gap between each of them and the separating surface 10. Consequently, it is preferred that each discharge pipe 43, 46 should be both adjustable in an axial direction and also angularly above the normal to the surface 10. The manner of support for each funnel and adjustment of each discharge pipe can be conventional.

Furthermore, one or both funnels 41, 44 may be replaced by pipes carrying the mixtures from centrifugal pumps under constant head conditions, or from other constant head supplies, the tank 32 and its associated funnels 34 then being rendered superfluous. Such an alternative arrangement permits a greater range of laminar flow velocities.

The separation process is extremely rapid, being completed for a pair of particles of different densities, in a small fraction of a second. The particle population per unit area of belt is an important factor, influenced by both belt speed and rate of feed. If the population is too dense, spatial separation of the constituents will not be sufliciently well developed. There is an optimum set of operating conditions for any given application which will provide the best separation; once fixed these conditions are easily maintained.

Small spatial separation of the low and high density ribbons A B potentially makes it difiicult to further separate them with a water jet. When a stream of water hits a flat surface there is always a flow of water backwards from the point of impact. Consequently, if a large jet is to be used to wash the light mineral to the sides of the belt there is a danger of this back-flow eroding the heavy mineral deposition. This difficulty is overcome by using a very fast belt speed to reduce the particle population density, and detecting the gap between the ribbons, possibly with a high-speed photocell seeker. This seeker would guide an extremely fine jet of water, the very small flow from which would be adequate to move the light particles and increase the spatial separation sufficiently to allow the introduction of a more voluminous flow of water a little further down the belt.

Referring now to FIGURES 3 and 4- of the drawings, which show a static machine, the separating surface is circular in plan, fiat and horizontal, and is made up of a central disc or table 70 and a concentric annulus 71. The disc and the annulus normally lie in a common plane to provide a continuous surface 72 on which separation takes place, but the central table 70 is vertically displaceable on a coaxial pillar 73 slidable in a guide sleeve 74 and supported at its lower end on a reciprocating mechanism exemplified as a lever 75 fulcrummed at 76 on a fixed support. The central table 70 slides in a cylindrical wall 77 which supports the inner periphery of the concentric annulus 71 and is open at its lower end to a heavy fraction discharge pipe 78. The meeting edges of the table 70 and annulus 71 are chamfered to ensure a tight fit and coplanar separating surfaces 72 when the table 70 is fully raised.

The outer circumference of the annulus 71 is supported on the frusto-conical inner wall 79 of an annular trough 80 whose outer wall 81 is cylindrical. The trough 80 has a narrow flat base 83 pierced at intervals by holes. Each hole may optionally be closed by a plug 84 (FIGURE 3). The trough is in turn encircled by a wall 85 which bounds a receptacle 86 having an outlet 87 for the light fraction.

Suspended coaxially above the table 70 with small clearance from the separating surface 72 is a mixture and water feed pipe 88 which delivers a quantity of the mixed particle slurry to the table 70 in a radial laminar flow pattern. Concentric with this jet or delivery pipe is an annular header 89 which is placed vertically above the zone which divides the heavy and light fraction ripples, and a depending flexible double-walled skirt 90 terminates at its lower edge just above the surface 72.

In operation, the table 70 is raised into its upper position flush with the annulus 71, and a slurry of the mixture to be separated is fed onto the centre of the surface 72 through the jet or delivery pipe 88. The slurry impinges on the separating surface and begins to spread radially outwards in a high thin lamina over the full 360, breaking down at a given radius into an annular standing wave from which the denser particles are deposited in the form of an annular ripple 91. As in the machine of FIG- URES l and 2, radial flow proceeds beyond the standing wave at a reduced and diminishing speed over the annular surface 71, the less dense fractions separating out in one or more further concentric ripples such as that shown at 92, while the water and any entrained particles flows on until it reaches the outer circumferential rim of the annulus 71, whence it falls into the trough 80 and, together with the entrained particles of normally unwanted light material and dust, is collected in the large receptacle 86, whence it is discharged through the drain 87. The machine is adjusted so that the dense ripple 91 is formed just inside the annular skirt 90.

While the dense particle ripple 91 is forming, it is preferable to disturb it gently by means of a manually or mechanically operated rake travelling in a circular path. Such a rake is shown in FIGURES 4 and 5 and consists of an arm 93 lying above and parallel to the surface 72 and carrying a number of depending prongs or tines 94 which just brush the separating disc surface lightly. The arm is supportetd on a sleeve 95 concentric with the feed pipe 88 and rotated slowly by some convenient mechanism (not shown).

When a suflicient quantity of the input mixture has been separated into the annular particle ripples 91, 92, the supply of slurry through the feed pipe 88 is cut off and the rake 93 is stopped. The central table 70 is then lowered on its pillar 73 (see FIGURE 4) and a curtain of water is fed through the double-walled skirt 90. The water impinges on the surface 72 in the zone between the ripples 91, 92 which is substantially free of particles, and spreads simultaneously radially outwards and inwards. The radially outward flow is of sufiicient velocity to carry the less dense particles outwards over the outer rim of the fixed annulus 71 into the trough 80, whence they can be drained off by the holes (under control of the plugs 84 if provided), while the radially inward flow carries the heavy particles inwards over the inner rim of the fixed annulus 71 into the chamber 77. Some particles will be washed down onto the retracted table 70 while others will fall to the bottom of the chamber through the clearance gap between the wall 77 and the circumferential edge of the table. To clear the former, a flow of water can be established through the feed pipe 88, or provision can be made for spinning the table 70 on its pillar 73. All the dense particles are discharged through the separate outlet 78'.

When the surface 72 has been cleared, the table 70 is raised to its upper position (see FIGURE 3) and the cycle of events is repeated. In this way, successive batches of mixed-particle material are treated to separate the denser fraction from the less dense fraction, irrespective of actual or relative particle sizes.

It will be understood that the rate and degree of separation achieved can be controlled by the rate of supply of slurry through the feed pipe 28, and furthermore, any contaminant particles which are lighter than the less dense fraction which forms the outer ripple '92 can be separated completely by being carried over into the trough 80 with the lateral stream. Effectively, therefore, a three-way split of the initial mixture can be achieved.

The machine shown in FIGURE 5 is a continuous separator generally similar to the machine of FIGURE 1 except that the mixture of particles is fed dryi.e., not as a slurry-to the top flight 10 onto a horizontal conveyor belt in the form of a ribbon 101 near one side edge of the belt. Thus, the input mixture may be available as a paste made up of liquid and the crushed or graded particulate ingredient and fed through a tubefor example, from a cyclone, elutriator or other dewatering device. A water or other process liquid header 102 runs beside and parallel to this edge, and three primary separation jet pipes 103, 104, extend horizontally towards the belt with their discharge ends overlying the separation surface 10 of the belt by increasing amounts in the direction of travel 11 of the belt. Each jet pipe is controlled by a respective valve 103a, 104a, 105:: for adjusting the rate of flow of the lateral stream established by each pipe across the separation surface 10.

Beyond the primary separation jet pipes are two secondary separation jet pipes 106, 107 and a concentration jet pipe 108, each controlled by a respective valve 106a, 107a, 108a.

A similar header (not shown) to the header 102 runs parallel to the opposite side edge of the belt 100 and supplies secondary separation jet pipes 109, counterpart to the pipes 106, 107, and a. concentration jet pipe 111 counterpart to the pipe 108, each also controlled by respective valves 109a, 110a, 111a.

Beyond the concentration jet pipes 108, 111, the con- 9 veyor belt 100 discharges onto two succeeding conveyor belts 112, 113, the belt 112 being relatively narrow and symmetrically collinear with the separation belt 100 whilst the belt 113 runs transverse to the line of the belt 100. The separating surface 10 of the belt 100 must be maintained as a flat plane over at least the zone between the primary separation jet pipe 103 and the concentration jet pipes 108, 111, and this zone may with advantage be supported on a smooth rubbing plate (not shown), or on jets of air or liquid, but the plane may slope as a whole. Beyond the concentration jet pipes 108-, 111, however, the belt may rise or fall to suit design convenience for the transfer of separated material to the succeeding belts 112, 113.

Although the flatness of the separation surface 10 is of prime importance, its texture and general inclination are less so. Thus, for example, the surface 10 may be smooth and polished or smooth but unpolished. It may be of a coarse texture, or provided with ridges, grooves, or sharp indentations of a magnitude and kind which would assist with the required development of standing waves and deposition of particles.

In operation, the conveyor belt 100 runs continuously at a controlled speed and the mixture is continuously fed to the belt as a wet or dry ribbon 101. The various valves 103a are opened to establish lateral laminar flow patterns of water across the surface 10, each breaking down at a predetermined zone in a standing wave. When the ribbon 101 encounters the standing wave from the first primary separation jet pipe 103 at the point of impingement on the surface 10, of the jet from the pipe 104, separate ripples 121, 122 begin to form. As the material progresses past the second and third primary jet pipes 104, 105, further separation-and lateral displacement-- of the ripples occurs at the points 115 and 116. The process can be repeated in any given case for as many times as the design of the machine permits until the required degree of particle separation has been achieved. Meanwhile, surplus water is discharged over the opposite edge of the belt 100, and either with or between the ribbons of solids.

At the point 117, the less dense fraction ripple 122 encounters the discharge from the first secondary separation jet pipe 106, and a further separation occurs into two ripples 122a, 121b, the former containing the less dense particles originally separated by the primary separation jets and the latter containing any dense particles which may have been carried over at the primary separation stages. Since these dense particles will normally consist predominantly of particles near the value at which separation occurs, a different jet velocity and/or mass rate of flow may be required at this point from that used in the primary separation stages. In similar manner, the dense particle ripple 121 will encounter, at 117a, the discharge from the first counterpart secondary separation jet pipe 109, and this discharge will be adjusted similarly to that of the pipe 106 to promote the separation of the heavier light fraction particles, or those light fraction particles which remained embedded in the heavy particle ripple 121, into a secondary light particle ripple 12112. The remainder of the heavy particles proceed in the heavy particle ripple 121a.

Further secondary separation may occur at the points 118, 11811, where the two light fraction ripples 122a, 122b, encounter the discharges from the pipes 107, 110 respectively, although the resultant separation will normally be marginal only and the main effect of these discharges will normally be the lateral displacement of the ripples 122a, 122b towards the respective edges of the belt 100.

Finally, the dense particle ripples 121a, 121b encounter, at 119 and 119a, the discharges from the pipes 108, 111 and are merged by lateral displacement into a single ribbon 1210 of heavy particles. This final ribbon is then discharged onto the collinear narrow belt 112 for delivery to the ultimate disposal point.

Meanwhile, the two less dense particle ripples 122a, 1221) are discharged on either side of the heavy ribbon 121a onto the transverse conveyor belt 113 for ultimate disposal.

As has already been noted, the speed of the separation belt is preferably controllable to suit the requirements of a particular operation, as also are the rates of discharge from the individual jet pipes. The latter may be constituted by flexible hoses which can be clamped in an optimum position lengthwise of the belt 100, and at an optimum height and angle. The pipe nozzles themselves preferably have wide, shallow apertures to produce a transverse oval-shaped laminar flow pattern.

A fixed plough may be used in place of the jet pipes 108, 111 (and 107, if desired) in order to effect the convergence or divergence, as the case may be, of any ripples. A fixed group of tines may also be suspended over the surface 10 for the mechanical disturbance of any ripple between any pair of separation jets.

The belt 100 may be located in a tank and may be submerged for part of its travel where it will be subjected to a cross-flow of water for the removal of fine contaminants, or for other treatment purposes.

The degree of stagger of the nozzles on the various pipes will probably vary from mixture to mixture, and the use of flexible hoses will facilitate the setting up of the machine for each feed.

Large grains of the heavy fraction will be the first to come to rest and may be ploughed off the belt after the first jet. Large grains of light material may then not move because the depth of water is not suificient to cover them and they may, with advantage, be separated mechanically while the smaller grains are washed from between them.

Small fines of both kinds may be sufficiently small to fioat off the belt without settling and yet may transport at sufficiently different rates to wash off separately to drains.

The following tests were made on a machine according to FIGURES 1 and 2 of the drawings.

(1) Sand/ coal mixtu*re.A sample of sand containing approximately 2% coal was fed to the feed funnel 41 of the machine. The sample was analysed as follows:

Percentage passing sieve Product Particle size B.S. mesh Feed Coal Sand The coal concentration in the residual sand was found to have been reduced to 0.053%. Separation of these constituents at the above initial feed concentration had not been found possible by other methods.

(2) Diamond-bearing sand.A sample of diamondbearing sand was passed once through the machine and a separation obtained. All the diamond values were found in the concentrate, and none were found in the tailings.

(3) Rutile/Silica mixture.-Rutile (titanium ore) is diificult to separate hydraulically from silica because of the high degree of smoothness of its particles, which results in their tending to behave identically with silica. Samples of rutile in a heavy concentration of about 30% in silica were passed through the machine. After the first pass, the concentration of rutile in the dense fraction was found to be about 85%.

(4) Wolframite c0ncentrate.-A sample of a Wolframite concentrate was received from a tin mine in Cornwall.

Further reduction of the tin content had not been possible with the equipment and processes employed at the mine. The sample contained 38% W and 10% Sn, with gangue minerals comprising silicates, micas and arsenopyrite (Fe content 25%).

During a series of tests a product was obtained containing 68.78% W0 and 2.99% Sn. Further experimental data was obtained by sizing the sample and processing the l00 mesh fraction. A concentrate, middlings, and tailings were drawn off; the middlings were fed back into the separator and the four value products sieved at 150 mesh and analysed. The results, reported in order of Wolfram gain, were:

These figures show that there is a shift of Wolfram towards the finer fractions and of tin to the coarser. Exploring this further, a sample of the l00 mesh material Was divided at 240 and 150 mesh; the result of processing was:

Percent Percent Wolfram Cassiterite Concentrate:

-240 mesh 67. 46 4. 82 65. 22 3. 05 56. 62 10. 00

indicating that there is a reduction of tin content at the -150 +240 mesh grading but a gain in the other fractions.

(5) Niobium ore c0ncentrati0n.The machine was fed with a sample of ground sovecarbonatyl containing 4.8% mixed ore consisting of Nb O magnetite and pyrites in approximately equal proportions. One pass gave a distinct separation of the ore from the gangue, and the ore concentration had risen to 65%. The ribbon of ore was about /s-inch wide and was separated from the gangue ribbon by /s-inch. The width of the gangue ribbon was 4 /z-inches. The primary standing wave from which the ore was deposited had an internal diameter of 8 inches and the ripple of gangue deposit had an internal diameter of 9 inches. There were no tailings.

The above results are typical of numerous tests made to establish the range of working conditions and optimum physical parameters of the machine, and serve to illustrate both its versatility as regards materials in the feed and potentiality for recovery of values from a wide range of concentrations some of which are well beyond the capabilities of conventional separation processesas when separating constituents of high density, of the order of 6 or 7. Such constituents cannot be separated by the use of high density liquids, and processes relying on the vapourisation of oils are both very expensive, due mainly to the large quantities of high cost oils required, and also limited by the range of oils available.

Machines according to the present invention, Whether of the continuous feed type as shown in FIGURES 1 and 2 and FIGURE 6 or of the batch type as shown in FIGURES 3-5, may be used either to produce the required end product-as in the case of the removal of coal from sandor as preliminary stages in a conventional separation process-as in the case of the concentration of highly diluted constituents.

Although the processing or carrier liquid will normally be water, it is to be understood that other mobile liquids may be used if preferred.

I claim:

1. The method of separating the constituents of a mixture of granular materials having different densities comprising projecting a jet of precessing liquid onto a generally horizontal plane separating surface at a substantially constant head through an orifice at a height not less than a given minimum value above the separating surface, both said head and said height being predetermined so as to produce an initial velocity and rate of free flow of the liquid over the said separating surface which exceeds a predetermined minimum such that, on impingement thereon, the liquid establishes a zone of free high speed laminar flow which breaks down at a finite distance from said orifice in a standing wave attern, and introducing the mixture of granular materials into the liquid in the orifice defining structure for selective deposition on the separating surface of the denser particles of the mixture.

2. The method according to claim 1 wherein the axis of the jet of the processing liquid is vertical so as to produce a circular zone of laminar fiow.

3. The method according to claim 2 wherein the rate of flow of the processing liquid is such as to initially entrain all particles in the feed mixture throughout the zone of laminar flow.

4. The method according to claim 1 including the step of raking the mass of denser particles deposited at the standing wave while subjected to the flow of processing liquid to liberate any less dense particles trapped therein.

5. The method according to claim 1 wherein the separating surface is traversed beneath successive jets of processing liquid, each arranged to established an independent free high speed laminar flow bounded by a respective standing wave pattern, and the starting mixture is fed t the liquid in the first orifice defining structure.

6. The method according to claim 1 wherein the separating surface is static and the mixture is fed into the jet of processing liquid in batches.

7. The method according to claim 6 wherein an annular curtain of liquid is directed downwards onto the separating surface at a boundary between zones of light and dense fraction particles after cessation of the said radially outward flow whereby to separate the two masses of particles.

8. A machine for separating the constituents of a mixture of granular starting materials having different densities utilizing the fluid properties of a processing liquid, comprising a generally horizontal plane separating surface, container means including a discharge orifice, means for feeding said mixture into said container means, means for introducing said processing liquid at a predetermined constant head into said container means, said orifice being located above said separating surface at a distance greater than a minimum value at which a throttling action is exerted on the jet of liquid emerging from said orifice sufficient to cause the emergent jet to establish a laminar fiow pattern terminating in a standing wave, and means for recovering at least the dense fraction of said mixture.

9. A machine according to claim 8 wherein a plurality of liquid discharge orifices are located at intervals above the separating surface along a common path for successive action on the material under treatment, and means is provided for effecting relative traverse of the discharge orifices and the separating surface in the direction of the said common path.

10. A machine according to claim 9 wherein the axis of at least one of said discharge orifices is oblique to the separating surface for the displacement of particles ,predominantly in a desired direction on the separating surface.

11. A machine according to claim 8 wherein the separating surface is a flight of a continuous belt, and means is provided for driving the belt at constant speed.

12. A machine according to claim 8 wherein the separating surface is a static table, a zone of which centred about the aXis of a liquid discharge orifice is vertically displaceable into a dense particle recovery chamber.

13. A machine according to claim 12 wherein an annular processing liquid discharge orifice is located above the relatively fixed zone bounding the displaceable zone of the static table at a radius greater than that of the standing wave.

14. A machine according to claim 8 wherein a mechanical rake is located above and displaceable relatively to the separating surface to agitate the dense particles deposited from the standing wave.

References Cited UNITED STATES PATENTS 1,359,105 11/1920 Richards 209-444 2,946,438 7/1960 Beluzou 209-156 2,946,439 7/1960 Condolios 209157 3,076,544 2/1963 Bodine.

OTHER REFERENCES Nature, vol. 211, No. 5051, pp. 813-816, Aug. 20, 1966, Radial Spread of a Liquid Stream on a Horizontal Plate, R. G. Olsson and E. T. Turkdogan.

FRANK W. LUTTER, Primary Examiner US. Cl. X.R. 209428 

